1. INFN - PadovaBeauty Measurements in pp with the Central Detector 1 Beauty Measurements in p-p with the Central Detector F. Antinori, C. Bombonati, A. Dainese, M. Lunardon and R. Turrisi Padova – University and INFN

2. INFN - PadovaBeauty Measurements in pp with the Central Detector 2 Luminosity Design Luminosity in pp @ 14 TeV: ~10 34 cm -2 s -1 Max Luminosity ~10 30 cm -2 s -1 Solution Enlarge the beam size Beam Size ~150  m vs. c  D 0 123  m and c  ~B 500  m Too much! Pile-up! 10 9 events in one LHC-year We need to optimize vertex reconstruction using the tracks

3. INFN - PadovaBeauty Measurements in pp with the Central Detector 3 Beauty Signal Semi-electronic channel B → e + X Branching Ratio = 21% –11% from b → B → e+X –10% from b → B → D → e+X Primary Vertex B e X d0d0 rec. track Yield bbbar couples 0.0072 B-mesons with an electron in acceptance 0.000756

4. INFN - PadovaBeauty Measurements in pp with the Central Detector 4 Background Sources 1.Charm decays (previous slide) 2.Charged Pions mis-identified as electrons 3.Photon conversions (  → e + e - ) in the beam pipe and inner layers 4.Decays of light mesons and Dalitz decays (mostly  0 )

5. INFN - PadovaBeauty Measurements in pp with the Central Detector 5 Detection Strategy 1. Electron Identification (TPC+TRD) (separation between e/  ) 2. Kinematical Cuts (in d 0 according to the p t bin) lowers  contamination to maximize B fraction Detection Strategy similar to that of Pb-Pb

6. INFN - PadovaBeauty Measurements in pp with the Central Detector 6 Primary Vertex Reconstruction in pp Tracking: tracks propagated to the nominal vertex position Vertex Finding: first estimate using all the couple of tracks Vertex Fitting: tracks propagated to the position calculated above, best vertex position from  2 minimization Results (A. Dainese and M. Masera) Vertex Resolution

7. INFN - PadovaBeauty Measurements in pp with the Central Detector 7 Selecting the Tracks for Vertexing VTX: vertex from the MC (for comparison only) ALL: no selection on the tracks OTHER: method that uses all tracks save the one for which the impact parameter is being calculated Resolution for d 0 (VTX) 1 ,3 ,5  : method that uses all tracks with d 0 < n  p t  where  is the d 0 -resolution and d 0 is calculated with respect to the primary vertex with no selection (ALL).

8. INFN - PadovaBeauty Measurements in pp with the Central Detector 8 Testing the Methods VTX p t > 1 GeV/c 1  loses 15 - 20% of the electron- tagged tracks. 3  and 5  lose less than 5% of the electron-tagged tracks. Method of Choice: 3  ALLOTHER 33 11 but … If an event has less than 3 tracks the primary vertex cannot be reconstructed Using only some of the tracks we are going to “lose” some events therefore

9. INFN - PadovaBeauty Measurements in pp with the Central Detector 9 Cross Section: How to In a certain p t -bin we get N “electrons”: N = N b + N c + N bkg 1. We subtract the contribution from charm: N – N c Charm calculated from D 0 measurement 2. We subtract the contribution from background: N b = (N – N c ) – N bkg Estimated from measured pions dN/dp t plus MC (including conversions) 3. We correct for acceptance/efficiency: dN b corr /dy = (N b /  ) Efficiency calculated with MC 4. We multiply by the inelastic pp cross section: d  e /dy =  pp. dN b corr /dy Cross section measured at LHC

10. INFN - PadovaBeauty Measurements in pp with the Central Detector 10 Errors Statistical Systematic Error from acceptance effect corrections (via MC): 10% (in principle p t -dependent) Error from subtractions: Rel. err. on bkg: 10% Rel. err. on charm: Error from inelastic cross section: 5% (p t -independent) d 0 cut affects we want a cut that minimizes both statistical AND systematic error

11. INFN - PadovaBeauty Measurements in pp with the Central Detector 11 Selecting the Cuts 2.5 < p t < 3 GeV/c7 < p t < 9 GeV/c12 < p t < 16 GeV/c At low-pt the systematic error dominates At high-pt the statistical error dominates

12. INFN - PadovaBeauty Measurements in pp with the Central Detector 12 Summary p t bin [GeV/c] |d 0 | cut [  m] 1 – 1.5400 1.5 – 2400 2 – 2.5300 2.5 – 3200 3 – 4150 4 – 5150 5 – 7100 7 – 9100 9 – 12100 12 – 1650 16 – 2050 Statistics (in 10 9 events)

13. INFN - PadovaBeauty Measurements in pp with the Central Detector 13 Statistics 11.56.59154 Stat. err. < 30% Statistical Error in different scenarios

14. INFN - PadovaBeauty Measurements in pp with the Central Detector 14 Cross Section Double-differential electrons cross section as measurable in 10 9 pp events. Inner bars show the statistical error while the outer bars show the quadratic sum of the statistical and systematic error. The 5% normalization error is not shown (p t -independent) Inner bars show the statistical error while the outer bars show the quadratic sum of the statistical and systematic error. The 5% normalization error is not shown (p t -independent). Using electrons in 2 < p t < 20 GeV/c obtain B meson 2 < p t min < 30 GeV/c MC-Based Procedure UA1-like Differential B-mesons cross section

15. INFN - PadovaBeauty Measurements in pp with the Central Detector 15 Conclusions Results –With 10 9 events: P t Range: 2-30 GeV/c Total P t -Dep. Error on Cross Section: 10-20% –Good physics even with the first 10 7 events To be done –Finalize methods for selecting the tracks –Integration of software in AliRoot

16. INFN - PadovaBeauty Measurements in pp with the Central Detector 16 EXTRA

17. INFN - PadovaBeauty Measurements in pp with the Central Detector 17 Statistics (expanded) Total Relative Error

18. INFN - PadovaBeauty Measurements in pp with the Central Detector 18 B-Meson Cross Section Using electrons in 2 < p t < 20 GeV/c obtain B meson 2 < p t min < 30 GeV/c MC-Based Procedure UA1-like